While the ophthalmoscope is useful in detecting early signs of diabetes, cardiovascular disease and other related conditions, obtaining a wide view of the interior of the eye and the periphery of the retina with this instrument generally requires that the iris be dilated. A more convenient tool for patient screening is provided by the non-mydriatic fundus camera which can be used as a diagnostic tool by ophthalmologists, optometrists and other medical professionals. Information is sought, for example, about the condition of the retina's dendritic pattern of blood vessels, the macula and the optic nerve among the main features of the fundus. The non-mydriatic camera attempts to focus a ring of light through the pupil to illuminate the retina without the need for dilation of the pupil. The ring of light diverges as it exits the posterior crystalline lens of the eye so that a large, defocused spot is formed on the retina. The return optical path between the fundus and the camera again traverses the crystalline lens The retinal image is acquired by the camera through the central hole in the ring of light.
Unfortunately, the retinal image obtained this way contains several major types of distortion. Some of these, such as distortion due to the camera and its optical system can be compensated by calibration with a standard test image. Others, arising in inaccessible portions of the optical path, such as intraocular reflections, haze in the vitreous humor, haze and flare due to a cataractous lens diffusing the peripheral ring of light into the central ‘viewing hole’, or corneal inhomogeneities, have not yielded to available image processing methods. In addition to the foregoing, and despite the use of strobed flash, images may be blurred as a result of axial movement of the patient's head, high velocity, micro-saccadic eye movements, or the operator's inability simultaneously to achieve all of the conditions necessary for a sharp image. Thus, the very eyes which require the highest level of diagnostic image quality (those exhibiting intraocular pathology) are the ones most likely to suffer from one or more of the foregoing image degradation problems. Accordingly, images obtained heretofore by conventional fundus cameras have suffered from an indeterminate amount of distortion and artifactual noise. It would be of inestimable value to be able to remove such distortions from the image acquired by a fundus camera.